1. Field of the Invention
The invention relates to RFID systems, operable with a variety of different dimensioned electro-magnetically coupled transponders, working at close proximity, to an RF transceiver antenna that is spatially selective for an individual transponder located in a predetermined transponder operating region to the exclusion of other adjacent transponders, and its application to printers-encoders or other systems utilizing such in UHF RFID systems.
2. Description of Related Art
UHF radio frequency identification (RFID) technology allows wireless data acquisition and or transmission from and or to active (battery powered) or passive transponders using a backscatter technique. To communicate with, i.e., “read” from and or “write” commands and/or data to a transponder, the transponder is exposed to an RF electromagnetic field by the transceiver that couples with and energizes (if passive) the transponder through electromagnetic induction and transfers commands and data using a predefined “air interface” RF signaling protocol.
When multiple passive transponders are within the range of the same RF transceiver electro-magnetic field they will each be energized and attempt to communicate with the transceiver, potentially causing errors in “reading” and or “writing” to a specific transponder in the reader field. Anti-collision management techniques exist to allow near simultaneous reading and writing to numerous closely grouped transponders in a common RF electro-magnetic field. However, anti-collision management increases system complexity, cost and delay response. Furthermore, anti-collision management is “blind” in that it cannot recognize where a specific transponder being processed is physically located in the RF electro-magnetic field, for example, which transponder is located proximate the print head of a printer-encoder.
One way to prevent errors during reading and writing to transponders without using anti-collision management is to electrically isolate a specific transponder of interest from nearby transponders. Previously, isolation of transponders has used RF-shielded housings and/or anechoic chambers through which the transponders are individually passed for personalized exposure to the interrogating RF field. This requires that the individual transponders have cumbersome shielding or a significant spatial separation.
RFID printers-encoders have been developed which are capable of on-demand printing on labels, tickets, tags, cards or other media with which a transponder is attached or embedded. These printer-encoders have a transceiver for on-demand communicating with the transponder on the individual media to read and/or store data into the attached transponder. For the reasons given, it is highly desirable in many applications to present the media on rolls or other format in which the transponders are closely spaced. However, close spacing of the transponders exacerbates the task of serially communicating with each individual transponder without concurrently communicating with neighboring transponders on the media. This selective communication exclusively with an individual transponder is further exacerbated in printers-encoders designed to print on the media in or near the same space as the transponder is positioned when being interrogated.
When transponders are supplied attached to a carrier substrate, for example in RFID-attached labels, tickets, tags or other media supplied in bulk rolls, Z-folded stacks or other format, an extra length of the carrier substrate is required to allow one transponder on the carrier substrate to exit the isolated field area before the next transponder in line enters it. The extra carrier substrate increases materials costs and the required volume of the transponder media bulk supply for a given number of transponders. Having increased spacing between transponders may also slow overall printer-encoder throughput.
When transponders of different sizes and form factors are processed, the RF shielding and or anechoic chamber configuration will also require reconfiguration, adding cost, complexity and reducing overall productivity. In certain printer-encoders it is desired to print on transponder-mounting media in the same transponder operating region in which the transponder is being read from or written to. This may be very difficult to accomplish if the transponder also must be isolated in a shielded housing or chamber.
UHF transponders may operate in, for example, the 902-928 MHz band in the United States and other ISM bands designated in different parts of the world. For example, in FIG. 1 a conventional one-half wavelength “Forward Wave” microstrip prior art coupler 3 consisting of a, for example, rectangular conductive strip 5 upon a printed circuit board 7 having a separate ground plane 9 layer configured for these frequencies. One end of the conductive strip 5 is connected to transceiver 42 and the other end is connected through terminating resistor 8 to ground plane 9. The conductive strip 5 as shown in FIG. 1 has a significant width due to RF design requirements imposed by the need to create acceptable frequency response characteristics. This type of prior art coupler 3 has been used with UHF transponders that are relatively large compared to the extent of prior art coupler 3.
As shown by FIGS. 2a and 2b, recently developed transponders 1, designed for operation at UHF frequencies, have one dimension so significantly reduced, here for example a few millimeters wide, that they will be activated upon passage proximate the larger prior art coupler 3 by electro-magnetic power leakage 10 concentrated at either side edge of the conductive strip 5 of prior art coupler 3. In FIG. 2A, the two leakage regions “A” and “B” defined by electro-magnetic power leakage 10 are small and relatively far apart, increasing system logical overhead and media conveyance positioning accuracy requirements. If the transponders 1 were placed close together, then multiple transponders 1 might be activated by the physically extensive one-half wavelength “Forward Wave” microstrip prior art coupler 3.
Thus the minimum required spacing of these transponders 1 to isolate them, and thus the minimum size of media 11 (assuming that they are embedded one per label or media 11 on carrier substrate 13) must be large relative to the size of the microstrip coupler 3. This creates issues for media suppliers by limiting the available space on the media 11 for transponder 1 placement and significantly increasing the necessary accuracy of the transponder 1 placement within and or under the printable media 11 and along the liner or carrier substrate 13. This also reduces the cost advantages of using the narrow dimensioned transponder(s) 1 within media 11, as the media 11 must be much larger than the transponder 1 to achieve adequate RF isolation.
Competition in the market for such “integrated” printer-encoder systems as well as other RFID interrogation systems has focused attention on the ability to interrogate with high spatial selectivity any transponder from a wide range of available transponders having different sizes, shapes and coupling characteristics as well as minimization of overall system, media size and transponder costs.
Therefore, it is an object of the invention to provide a device, systems and methods that overcome deficiencies in such prior art.